Numerical studies on vortex-induced motions of a multi-column deep-draft oil and gas exploration platform

This paper presents numerical studies on vortex-induced motions (VIM) of a multi-column floating oil and gas exploration platform. Numerical computations are performed using an improved delayed detached eddy simulation (IDDES) together with a moving grid approach. The transverse (sway) and yaw motion responses, motion trajectories, motion frequencies and power spectral density of motions are computed and analyzed systematically. After extensive comparisons with experiments, it is confirmed that the present numerical solutions using IDDES agree well with the experimental results and are better than those via delayed detached eddy simulation (DDES). The differences of transverse motion responses between computational results and experiments are less than 10% in the lock-in region. The numerical simulations reveal that the transverse VIM responses occur in a range of reduced velocities from 7.0 to 14.0 at H/D = 1.44 (H and D are the column height and width, respectively). The largest nominal transverse amplitude, around 35% of the column width, occurs for 22.5∘ current incidence. It is found that the VIM responses mainly perform along the platform diagonals for 15∘, 22.5∘ and 45∘ current incidences. The transverse and yaw motion frequencies for 15∘, 22.5∘ and 45∘ current incidences are higher than those for 0∘ current incidence. The energy levels of the yaw motion responses for 15∘, 22.5∘ and 45∘ current incidences are about 10% of that for 0∘ current incidence. Moreover, parametric studies have been performed to examine the effect of submerged column height on VIM. It demonstrates that VIM in transverse direction grows significantly when submerged column height H/D is greater than 1.0. To be more specific, compared to the case with H/D = 1.44, VIM in transverse direction at H/D = 3.0 increase by around 120%.